A digital output circuit disconnection diagnosis device and a diagnosis method

Abstract

The present invention discloses a digital quantity output circuit disconnection diagnosis device, comprising: a DC power supply; two MOS switches connected in series, a front-stage MOS switch K1 and a rear-stage MOS switch K2; the DC power supply outputs a power supply positive voltage and a driving current after passing through the front-stage MOS switch and the rear-stage MOS switch in sequence; an external load is connected to a cable to be diagnosed, and the driving current returns to the ground after passing through the load; a controller sends a high or low level control signal, and controls the closing and closing of the two series-connected MOS switches respectively through a corresponding signal isolator; a disconnection detection module is connected in parallel with the front-stage MOS switch, and outputs a digital signal to the controller. The diagnostic device of the present invention can detect the cable disconnection fault in time when the external load is powered on or off, and the technology adopts switch quantity detection, which is low in cost and can meet the application of a large load variation range.

Description

Technical Field

[0001] The invention relates to a cable circuit diagnosis and implementation method of a digital quantity output loop in an automation product. Background Art

[0002] In industrial automation production applications, DCS and PLC products are widely used. If the digital output modules are to be able to output signals to drive the equipment normally, cable break diagnosis is essential. The traditional digital output cable diagnosis solution uses a series current sensing resistor to differentially collect the current signal of the loop to an analog-to-digital converter, or convert it into a voltage signal for a comparator to judge and identify.

[0003] However, when the external load varies greatly, the current in the loop will also vary greatly. In order to ensure the normal operation of the diagnostic function, high-precision devices are required to complete the identification, which greatly increases the hardware cost. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a digital output circuit break diagnosis device and diagnosis method, which can promptly detect the cable break fault when the external load is powered on or off. The technology adopts switch quantity detection, which has low cost and can meet the applications with a large load variation range.

[0005] The technical solution provided by the present invention is as follows:

[0006] A digital output circuit disconnection diagnosis device, comprising:

[0007] DC power supply;

[0008] Two MOS switches are connected in series, namely, the front-stage MOS switch K1 and the rear-stage MOS switch K2; the DC power supply outputs the positive voltage and driving current of the power supply after passing through the front-stage MOS switch and the rear-stage MOS switch in sequence; the external load is connected to the cable to be diagnosed, and the driving current returns to the ground after passing through the load;

[0009] The controller sends out a high or low level control signal to control the closing and closing of two MOS switches in series through corresponding signal isolators;

[0010] The disconnection detection module is connected in parallel with the preceding MOS switch and outputs a digital signal to the controller.

[0011] More specifically, the positive end of the DC power supply is connected to the s-pole of the front-stage MOS switch, the d-pole of the MOS switch is connected to the s-pole of the rear-stage MOS switch, the d-pole of the rear-stage MOS switch is connected to the diagnosed cable and outputs the positive voltage of the power supply and the driving current, the external load is connected to the diagnosed cable, the driving current flows into the load from the positive end of the load, flows out from the negative end of the load and returns to the ground;

[0012] The output IO port of the controller is connected to the input end of the signal isolator and sends a high or low level control signal to the signal isolator. The output ends of the two signal isolators are respectively connected to the g poles of the two MOS switches; the disconnection detection module is connected to the s pole and d pole of the previous MOS switch, and the disconnection detection module outputs a digital signal to the IO port of the controller.

[0013] Furthermore, the power supply is DC 24V or DC 48V.

[0014] Furthermore, the two MOS switches are both PMOS. When the gate and source voltages of the MOS switch are 0, the MOS switch is turned off; when the gate and source voltages of the MOS switch are less than 0, the MOS switch is turned on; the controller controls the subsequent MOS switch to close or close, and the load is powered on or off accordingly. When the subsequent switch remains closed, the controller controls the previous switch to close or close, and the disconnection detection module outputs an identification signal to the controller input port.

[0015] Furthermore, in the disconnection detection module, the key component is an optical coupler, the input end of the optical coupler is connected in series with a current limiting resistor and then connected in parallel with the s pole and d pole of the previous stage MOS switch, and the output end of the optical coupler is connected to the input IO port of the controller. When the previous stage and the next stage MOS switches are closed, the voltage drop of the previous stage MOS switch is very small, there is almost no current at the input end of the optical coupler, and the output of the optical coupler is turned off. The next stage MOS switch remains closed, and when the previous stage MOS switch is turned off, current flows through the optical coupler, and the output end of the optical coupler is closed.

[0016] Furthermore, the signal isolator is an optical coupler, the input end of the optical coupler is connected to the controller output IO port, and the output end of the optical coupler is connected to the g pole of the MOS switch.

[0017] The present invention also provides a method for diagnosing a disconnection in a digital output circuit, comprising:

[0018] 1) When the external load is normally powered, the controller controls the front-stage MOS switch K1 and the rear-stage MOS tube K2 to remain closed, and the disconnection detection module U4 outputs the shutdown. During the diagnosis process, the controller controls K1 to be closed and closed regularly. If the external cable is normal, U4 will output the closing and shutoff signals to the controller input port accordingly. If the external cable is disconnected, U4 will constantly output the shutdown signal. The duration of K1 shutdown is very short, less than 2ms, and will not affect the normal operation of the load;

[0019] 2) When the external load is normally powered off, the controller controls K1 and K2 to remain disconnected, and the disconnection detection module U4 outputs shutdown. During the diagnosis process, the controller controls K2 to be regularly closed and closed. If the external cable is normal, U4 will output the shutdown and closing signals to the controller input port accordingly. If the external cable is disconnected, U4 will constantly output the shutdown signal. The duration of K2 closure is very short, less than 2ms, and will not affect the normal operation of the load.

[0020] The beneficial effect of the present invention is that when the device is working, the cable can be diagnosed online continuously and regularly, and an alarm can be given in time when a fault occurs, regardless of whether the external load is working in a powered or unpowered state. The invention is applicable to a large external load range, from 4mA to 1A, and the cost of implementation is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of the structure of the diagnostic device of the present invention;

[0022] Figure 2 for Figure 1 Detailed schematic diagram of the signal isolator U2 or U3;

[0023] Figure 3 for Figure 1 Detailed schematic diagram of the interrupt line detection module U4. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings.

[0025] like Figure 1 The present invention discloses a digital output circuit disconnection diagnosis device, comprising a DC power supply Vcc, a controller U1, signal isolators U2 and U3, a front-stage PMOS switch K1, a rear-stage PMOS switch K2, and a disconnection detection module U4, which is connected to a diagnosed cable and an external load R to perform cable disconnection diagnosis.

[0026] like Figure 2 , signal isolator U2 or U3, using optocoupler, the positive input terminal is connected to the controller IO port, and the negative input terminal is connected to the ground of controller U1. The negative output terminal is connected to the ground of DC power supply Vcc. The positive output terminal is connected to two series resistors R3 and R4, and then connected to the positive end of the DC power supply. The connection point of the two series resistors is connected to the g pole of the corresponding PMOS switch. As the optocoupler is turned on and off, the voltage of Vg will also change.

[0027] like Figure 3The disconnection detection module U4 includes a key component, an optical coupler K3. The positive end of the input side of K3 is connected to a current limiting resistor R2 with a resistance of 2KΩ. The other end of R2 is connected to the s-pole of the previous MOS switch K1. The negative end of the input side of K3 is connected to the d-pole of the previous MOS switch K1. The input sides of K1 and K3 form a parallel relationship. The negative end of the output side of K3 is connected to the ground of the controller U1, and the positive end of the output side is connected to the pull-up resistor R1, and the controller IO port is input at the same time. The pull-up resistor is connected to the positive end of the controller power supply.

[0028] The input side current range of the optocoupler K3 is 1mA to 50mA to conduct normally, and the voltage drop of the internal diode at the input end of K3 is about 1V when conducting. The on-resistance of the previous MOS switch is 0.1Ω. When the two MOS switches K1 and K2 of the loop are closed, the load is energized, and the maximum allowable current of the loop design is 1A. Since the current limiting resistor R2 on the input side of K3 is 2KΩ, the minimum conduction current is 1mA, and the maximum voltage drop of the previous MOS switch is only 0.1V, and the voltage drop of the diode at the input end of K3 is not taken into account, the current on the input side of K3 is much less than 1mA, and the output side is turned off.

[0029] The load design allows a current range of 4mA to 1A, a DC power supply voltage of 24V or 48V, and a load resistance range of 24Ω to 6KΩ or 48Ω to 12KΩ. The controller controls the front-stage MOS switch K1 to turn off, and the rear-stage MOS switch K2 remains closed: when the DC power supply is 24V, the current range on the input side of K3 is about 3mA to 12mA; when the DC power supply is 48V, the current range on the input side of K3 is about 6mA to 24mA, which is within the input current range when K3 is turned on, meeting the output conduction requirements of K3, and can complete the disconnection diagnosis function.

[0030] When performing cable diagnosis, when the external load is normally powered on, the controller controls the subsequent MOS tube K2 to remain closed, and controls K1 to be periodically turned off and closed; when the external load is normally powered off, the controller controls K1 to remain open, and controls K2 to be periodically turned off and closed.

[0031] If the external cable is normal, U4 will output closing and closing signals to the controller input port accordingly; if the external cable is broken, U4 will constantly output closing signals.

[0032] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A digital output circuit disconnection diagnosis device, characterized in that: include: DC power supply; Signal isolator; Two MOS switches connected in series, a front-stage MOS switch and a rear-stage MOS switch; The DC power supply outputs the positive voltage and driving current of the power supply after passing through the front-stage MOS switch and the rear-stage MOS switch in sequence; the external load is connected to the cable to be diagnosed, and the driving current returns to the ground after passing through the load; The controller sends out a high or low level control signal to control the closing and closing of two MOS switches in series through corresponding signal isolators; The disconnection detection module is connected in parallel with the previous MOS switch and outputs a digital signal to the controller; The digital output circuit disconnection diagnostic device performs diagnosis by the following method: When the external load is normally powered, the controller controls the front-stage MOS switch and the rear-stage MOS switch to remain closed, and the output of the disconnection detection module is turned off; During the diagnosis process, the controller controls the front-stage MOS switch to be turned off and on periodically, and the controller receives the identification signal of the disconnection detection module to perform cable diagnosis: when the disconnection detection module outputs the closing and shutting down signals correspondingly, the external cable is diagnosed to be normal; when the disconnection detection module outputs the shutting down signal constantly, the external cable is diagnosed to be disconnected; When the external load is normally in a power-off application, the controller controls the front-stage MOS switch and the rear-stage MOS switch to remain disconnected, and the output of the disconnection detection module is turned off; During the diagnosis process, the controller controls the subsequent MOS switch to be turned off and closed periodically, and performs cable diagnosis by receiving the identification signal of the disconnection detection module through the controller: when the disconnection detection module outputs the closing and shutting down signals accordingly, the external cable is diagnosed to be normal; when the disconnection detection module constantly outputs the shutting down signal, the external cable is diagnosed to be disconnected.

2. The digital output circuit disconnection diagnosis device according to claim 1, characterized in that: The front-stage MOS switch and the rear-stage MOS switch both use PMOS; when the gate and source voltages of the MOS switch are 0, the MOS switch is turned off; when the gate and source voltages of the MOS switch are less than 0, the MOS switch is turned on; when the external load is powered on, the controller controls the rear-stage MOS switch to remain closed, and controls the front-stage MOS switch to be closed and turned off periodically; when the external load is powered off, the controller controls the front-stage MOS switch to remain closed, and controls the rear-stage MOS switch to be closed and turned off periodically; The controller controls the preceding MOS switch or the succeeding MOS switch to be turned off for a duration of less than 2 ms.

3. The digital output circuit disconnection diagnosis device according to claim 2, characterized in that: The disconnection detection module adopts an optical coupler, the input end of the optical coupler is connected in series with a current limiting resistor and then connected in parallel with the s pole and d pole of the previous stage MOS switch, and the output end of the optical coupler is connected to the input IO port of the controller.

4. The digital output circuit disconnection diagnosis device according to claim 3, characterized in that: The signal isolators all use optical couplers, the input end of the optical coupler is connected to the output IO port of the controller, and the output end of the optical coupler is connected to the g-level of the corresponding MOS switch.

5. The digital output circuit disconnection diagnosis device according to claim 4, characterized in that: The DC power supply adopts DC 24V or DC 48V.

6. The digital output circuit disconnection diagnosis device according to claim 5, characterized in that: The current limiting resistor connected in series with the optical coupler of the disconnection detection module is 2KΩ.

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